CCP-CPP GMR read heads are considered as promising candidates for 180 Gb/in2 and higher magnetic recording densities. This increase in recording density requires the reduction of the read head dimensions. For example, for 180 Gb/in2, dimensions around 0.1×0.1 microns are required. A CPP read head can be considered functional only if a significant output voltage, Vout, can be achieved when the head senses the magnetic field of a recorded medium. If DR/R is defined as the percentage resistance change, at constant voltage, under the magnetic field for the sensor and V is the voltage applied across the sensor (BHV), then Vout=DR/R×V.
Almost all attempts by the prior art to increase Vout have focused on ways to increase film DR/R since it has been assumed that V was already at its maximum value, any further increases being expected to lead to unacceptable increases in the operating temperature of the device. In particular, said increases in temperature would occur within the current confined paths (see 15 in FIG. 1) and/or due to breakdowns within the nano-oxide layer. Since DR/R decreases with temperature, this implied a reduced Vout as well as severe reliability problems. The present invention is directed to ways to increase Vout without raising the operating temperature of the device above acceptable levels.
Referring now to FIG. 1, we show there the main features of a CCP-CPP GMR read head device. These are an antiferromagnetic (pinning) layer 12, which may include a a seed layer (not shown), pinned layer 14 (usually a tri-layer that acts as a synthetic AFM, but shown here as a single layer), a non-magnetic spacer layer 15 (which will be discussed further below), a free layer 16 and a capping layer 17 which may include a metallic gap layer (also not shown) directly below layer 11b. 
When the free layer is exposed to an external magnetic field, the direction of its magnetization is free to rotate according to the direction of the external field. After the external field is removed, the magnetization of the free layer will stay at a direction, which is dictated by the minimum energy state, determined by the crystalline and shape anisotropy, current field, coupling field and demagnetization field. If the direction of the pinned field is parallel to the free layer, electrons passing between the free and pinned layers, suffer less scattering. Thus, the resistance at this state is lower. If, however, the magnetization of the pinned layer is anti-parallel to that of the free layer, electrons moving from one layer into the other will suffer more scattering so the resistance of the structure will increase. The change in resistance of a spin valve is typically 5-15%.
In the foregoing discussion it was tacitly implied that non-magnetic spacer layer 15 is a homogenous layer of a single conductive material. In the CCP (current confined path) design, the spacer layer is actually a trilayer of two conductive layers (such as copper) with a very thin insulating layer (usually a nano-oxide layer) between them. The latter is typically between about 5 and 15 Angstroms thick, deliberately providing metal paths within itself. Thus, current through the spacer layer is confined to those areas where the two conductive layers contact one another via these metal paths (shown schematically in FIG. 1 as the hatched areas within layer 15).
It can be seen in FIG. 1 that current enters the device through lead 11a and exits through lead 11b (or vice versa if convention demands). It is, in general, preferable for 11a and 11b to be formed from the same material, most typically copper or gold, selected for their high electrical conductivity. In U.S. Patent Application 2004/0233584 (Liu et al), assigned to a common assignee as the current invention, it was shown that it can be advantageous, where feasible, to have top and bottom leads made of materials that have different thermoelectric powers, resulting in effective cooling of the GMR stack.
In a CCP device, RA (the resistance area product) can be adjusted in the range of 0.2-0.5 ohm.μm2, compared to uniform metal spacer devices where RA is typically in the range 0.05-0.1 ohm.μm2. As a consequence, DR/R can be improved to a level much higher than that attainable by a ‘metallic’ CPP device.
The down side of CCP designs is that the current density in the confined path can be much higher than the average current density. As a result, the spacer will be a hot spot during operation. Since DR/R is known to decrease with rising temperature, it becomes very important to cool the spacer during operation in order to extract the best possible performance from the device.
A routine search of the prior art was performed with the following references of interest being found:
U.S. Pat. No. 6,353,318 (Sin et al) discloses top and bottom leads made of the same material. In U.S. Pat. No. 6,597,544, Ghosal shows a cold plate thermally coupled to a thermoelectric cooler. U.S. Patent Application 2005/0052789 (Zhang et al), a Headway application, also shows the use of thermoelectric cooling leads. U.S. Pat. No. 5,627,704 (Lederman et al) and U.S. Pat. No. 5,668,688 (Dykes et al) show CPP mode read heads.